Lead author Fabio Cirignotta, M.D., professor of neurology at the University of Bologna in Italy, said that the only effective countermeasure to drowsiness is to stop driving immediately, pull over to a safe place and nap for 10 to15 minutes.

Antihistamines: These drugs prevent histamine from binding on the receptors of immune cells and can help prevent and treat allergic symptoms, including sneezing and runny nose, but can also cause side effects such as drowsiness and dry mouth.